(1) Field of the Invention
This invention relates to a dielectric resonator mainly for use in a portable transceiver in a frequency range of several hundred megahertz to several gigahertz and a manufacturing method thereof
(2) Description of the Prior Art
Among known resonators used in a frequency range of several hundred megahertz to several gigahertz are a dielectric resonator which has been proposed by the inventors of this invention (illustrated in FIGS. 1a, 1b and 1c) and a helical resonator shown in FIG. 3.
FIG. 1a is a front view of the dielectric resonator, FIG. 1b is a side view thereof, and FIG. 1c is a rear view thereof. In these figures, a dielectric plate 51 formed of FROR or the like has an upper surface 51a and a lower surface 51b. A set of capacitor electrodes 52a and 52b and another set of capacitor electrodes 53a and 53b are formed on the upper and the lower surfaces 51a and 51b, respectively. An inductor electrode 54a is formed on the upper surface 51a to connect 52a and 52b, and another inductor electrode 55a is formed on the lower surface 51b to connect 53a and 53b. The above electrodes are formed by screen-printing a silver paste on the surfaces.
The above two sets of electrodes are opposed to each other with the dielectric plate 51 therebetween, thereby forming capacitors C1 and C2, whose capacitances depend on the dielectric constant and the thickness of the dielectric plate 51 and on the surface area where the one of the sets oppose the other.
FIG. 2 is an equivalent circuit of the dielectric resonator, where L1 and L2 indicate inductors formed by the inductor electrodes 54a and 55a, respectively. In FIG. 2, an LC series circuit consisting of the capacitor C1 and inductors L1 and L2 connected to both ends thereof is connected to the capacitor C2 in parallel.
FIG. 3 shows the above-mentioned helical resonator, in which a helical coil 21 wound around the insulating cylinder 23 is cased in a metal container 22. An inductance of the helical coil 21 and a capacitance formed between the helical coil 21 and the metal container 22 constitute an LC resonator.
Both the dielectric resonator of FIG. 1 and the helical resonator of FIG. 3 have problems. The former needs a shield due to its vulnerability to the outer electromagnetic field. However, the fact that the shield should be a metal plate and should be provided a specified distance away from the capacitor electrodes and the inductor electrodes inevitably increases the size of the resonator.
In the latter, the metal container 22 acts as a shield. However, the helical resonator is difficult to be compact and is not suitable for surface mounting.